Summary

We investigated if the equilibrium theory of island biogeography (ETIB) can be applied to the meiofauna of groundwater-fed springs. We tested if copepod species richness was related with spring area, discharge and elevation. Additionally, five hypotheses are tested based on species distribution patterns, dispersal ability and life-history characteristics of several guilds (stygobiotic, non-stygobiotic, cold stenotherm and non-cold stenotherm species). Thirty springs in the Central Apennines (Italy) were considered. A multimodel selection procedure was applied to select best fit models using both ordinary least squares regressions and autoregressive models. Mantel tests were used to investigate the impact of spatial autocorrelation in determining inter-spring similarity (ßsor), pure turnover (ßsim), inter-site nestedness (ßnest = ßsor-ßsim) and matrix nestedness (measured by using NODF and other metrics). Explicit consideration of spatial correlations reduced the importance of predictors of overall species richness, non-cold stenotherm species (both negatively affected by elevation), cold stenotherm species, and non-stygobiotic species, but increased the importance of area for the stygobiotic species. We detected nested patterns in all cases, except for the stygobites. Inter-spring distances were positively correlated with ßsor and ßnest (but not with ßsim) for the entire data set and for non-stygobiotic, cold stenotherm and non-cold stenotherm species. In the case of stygobites, inter-spring geographical distances were marginally correlated with ßsor and no correlation was found for ßsim and ßnest. We found support for ETIB predictions about species richness, which was positively influenced by area and negatively by elevation (which expresses the size of source of immigrants). Low turnover and high nestedness are consistent with an equilibrium scenario mainly regulated by immigration and extinction. Stygobites, which include many distributional and evolutionary relicts, have a low capability to disperse through the aquifers and tend to be mainly confined to the springs where they drifted out and were trapped by springbed sediments.